Embryonic Development: 4-8 weeks of embryo development.

4th Week Complete mass (baby and chorion, etc.) - about 1" long and the size of a pigeon's egg.
Embryo inside is about 3/8" and weighs less than 1 gram.
Outpouching from anterior brain - early eyes - limb buds of arms and legs.

8th Week Major organs begin development.
Now about size of hen's egg.
Embryo is 1" long and about 4 grams.
Hands and feet are seen.
Baby is extremely reactive to its environment.
Male sex hormone (testosterone) produced by testes
Masculine development in males - no change in females.

12th Week Embryo is about the size of a goose egg.
Placenta is well established and weighs more than the baby.
Baby is approximately 3 1/2" long and weights about 60 grams (2 oz.). Fingers and toes can be seen.
This is the end of the embryonic stage.

28th Week Baby can survive outside uterus if lungs capable of breathing.
10-20% survival if born at this time.
14", 2 1/2 lbs.
Viable (legally).
Fetus in breech position until 32nd week.

32nd Week Maturing. 50% survival if born at this time.
Should turn to head down position.
16", 3 1/2 lbs. (1680 grams).
Skin is red and wrinkly.
The downy type hair is less plentiful and has more vernix.

30-34th Week Baby is the same size as placenta.

36th Week 94% survival rate if born at this age.
18", 5 1/2 lbs.
Has some subcutaneous fat.
The baby stores things during this last trimester.
Mother should watch her weight at this time.
Fingernails are now at the tips of the fingers.